A flak jacket (or "tea-caddy") protective cover for spent nuclear fuel casks of the type containing spent nuclear fuel rods, and the like. Conventionally, the storage casks are cylindrical iron containers, approximately eight feet in diameter and eighteen feet in height. The casks are stored on site at nuclear generating facility, either in a pond or they are stacked above ground. In either case, the vulnerability of the casks to terrorist attack is manifest.